1) Field of the Invention
The invention relates to rotary brushless electrical motors. More particularly, the invention relates to a motor having magnetically isolated stator sections.
2) Description of the Prior Art
In traditional configurations of brushless electrical motors having a stator with coiled stator teeth and a rotor with permanent magnet poles, coils are driven by multiple phases and phases overlap one another on stator teeth. U.S. Pat. No. 4,774,428 to Konecny describes a rotary motor configuration where coils driven by the same phase are grouped on proximate teeth to occupy one distinct portion of the stator. Konecny explains that this phase grouping reduces electromagnetic torque ripple and increases starting torque per unit of volume of wire. This motor have a single stator magnetic circuit with teeth substantially equidistantly distributed. In this winding configuration, one coil is wound around each tooth.
Konecny teaches a rule for selecting the number of stator teeth and rotor poles that minimizes the magnitude of cogging torque for a three-phase motor having a single stator magnetic circuit. The number of stator teeth is given by 3(2n+1) and the number of rotor permanent magnets by 3(2n+1)±1, where n is a positive integer.
U.S. Pat. No. 4,754,207 to Heidelberg, U.S. Pat. No. 6,384,496 to Pyntikov et al. and U.S. Pat. No. 6,492,756 to Maslov et al. expose the advantages of isolating each phase group of coils into separate sections. Magnetic material of each stator section is magnetically isolated from the other sections and each section carries coils driven by the same phase. Isolation of magnetic circuit of each phase reduces mutual inductance between phases and cyclic inductance.
U.S. Pat. No. 4,754,207 to Heidelberg et al. presents a motor configuration wherein adjacent stator teeth are grouped into sections, each section holding one phase. Heidelberg teaches a motor configuration wherein the angular distance between adjacent stator teeth within one section is equal to the angular distance between the rotor permanent magnets and the angular distance between adjacent stator teeth belonging to distinct adjacent sections is 1.6 times the distance between adjacent poles within one section.
Previous configurations of brushless electrical motor with stator sections present somewhat high magnitude of cogging torque which causes undesirable motor vibrations. There is thus a need for a simply constructed electrical motor with low magnitude of cogging torque which the prior arts have not completely fulfilled.